Publications
142 results found
Nguyen HGT, Toman B, van Zee RD, et al., 2023, Reference isotherms for water vapor sorption on nanoporous carbon: results of an interlaboratory study, Adsorption, Vol: 29, Pages: 113-124, ISSN: 0929-5607
This paper reports the results of an international interlaboratory study sponsored by the Versailles Project on Advanced Materials and Standards (VAMAS) and led by the National Institute of Standards and Technology (NIST) on the measurement of water vapor sorption isotherms at 25 °C on a pelletized nanoporous carbon (BAM-P109, a certified reference material). Thirteen laboratories participated in the study and contributed nine pure water vapor isotherms and four relative humidity isotherms, using nitrogen as the carrier gas. From these data, reference isotherms, along with the 95% uncertainty interval (Uk=2), were determined and are reported in a tabular format.
L'Hermitte A, Azzan H, Yio MHN, et al., 2023, Effect of surface functionalization on the moisture stability and sorption properties of porous boron nitride, Microporous and Mesoporous Materials, Vol: 352, Pages: 1-13, ISSN: 1387-1811
Porous boron nitride (BN) is a promising adsorbent owing to its high surface area and porosity, as well as thermal and oxidative stability. It has been explored in the past decade for applications in gas and liquid separations, such as CO2 capture and water cleaning. However, the material has displayed hydrolytic instability. Owing to the presence of moisture in most industrial settings, whether it is for storage or cyclic adsorption processes, ensuring the moisture stability of an adsorbent is crucial. While this topic has been researched for other adsorbents such as zeolites and metal organic frameworks (MOFs), little is known on controlling the hydrolytic stability of porous BN. In this study, we propose a method to enhance porous BN's hydrolytic stability via surface functionalization using a fluoroalkylsilane. We explored two different routes of functionalization: (i) functionalization of porous BN powder followed by pelletization (route 1) and (ii) coating of porous BN pellets with fluoroalkylsilane (route 2). Spectroscopic, analytical and imaging techniques confirmed the functionalization process qualitatively and quantitatively. We subjected the functionalized samples to moisture exposure at 54% RH (similar to common storage conditions) and 92% RH (similar to flue gas stream conditions with high moisture content), and characterized them to probe their resistance to moisture. We also investigated their equilibrium and kinetic sorption properties in the context of CO2/N2 separation. Both routes produced materials with enhanced moisture stability. However, we noted differences between both functionalization routes. Route 2 produced a sample with a higher grafting yield and hydrophobic nature, and therefore better resistance to moisture exposure than route 1. From a sorption point of view, despite reduced porosity, the functionalized samples maintain reasonable CO2 uptakes. The functionalization led to changes in the textural features of the samples, which cause
Mistry EDR, Lubert-Perquel D, Nevjestic I, et al., 2023, Paramagnetic States in Oxygen-Doped Boron Nitride Extend Light Harvesting and Photochemistry to the Deep Visible Region., Chem Mater, Vol: 35, Pages: 1858-1867, ISSN: 0897-4756
A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered. Here, using an integrated experimental and first-principles-based computational approach, we demonstrate that paramagnetic isolated OB3 states are paramount to inducing prominent red-shifted light absorption. Conversely, we highlight the diamagnetic nature of O-B-O states, which are shown to cause undesired larger band gaps and impaired photochemistry. This study elucidates the importance of paramagnetism in BNO semiconductors and provides fundamental insight into its photophysics. The work herein paves the way for tailoring of its optoelectronic and photochemical properties for solar fuel synthesis.
Itskou I, L'Hermitte A, Marchesini S, et al., 2023, How to Tailor Porous Boron Nitride Properties for Applications in Interfacial Processes, ACCOUNTS OF MATERIALS RESEARCH
Low M-YA, Barton LV, Pini R, et al., 2023, Analytical review of the current state of knowledge of adsorption materials and processes for direct air capture, Chemical Engineering Research and Design, Vol: 189, Pages: 745-767, ISSN: 0263-8762
Significant research interest has been directed towards the deployment of direct air capture (DAC) as a net-negative CO2 emissions technology to help limit global temperature rise to below 2 °C. The scope of this review is to outline the advancement of adsorption-based DAC technologies, as well as to highlight the still-existing data gaps, for both materials’ development and process design in the period 2016 – 2021. On the material side, we highlight the available and missing data on adsorbent properties in relation to what is needed for process modelling and design. We cover material densities, textural properties, thermal properties, adsorption isotherms (i.e. CO2, N2, O2, H2O), adsorption kinetics, and adsorbent stability towards humidity, oxidation, and cycling. On the process side, we provide a detailed look at key process studies conducted in the same time frame by considering the trade-offs to be expected in the design of the adsorption-based DAC process. We focus on process configuration and contactor design, desorption processes, and the need for systematic reporting of key performance indicators to allow for accurate comparisons and benchmarking. Throughout the review, we identify the lack of synergy between material and process development which must be addressed to advance the field of DAC by adsorption.
Xiong Y, Tian T, L'Hermitte A, et al., 2022, Using silver exchange to achieve high uptake and selectivity for propylene/ propane separation in zeolite Y, Chemical Engineering Journal, Vol: 446, ISSN: 1385-8947
Adsorptive separation of propylene and propane, an important step of polypropylene production, is more energy-efficient than distillation. However, the challenge lies in the design of an adsorbent which exhibits both high selectivity and uptake. Herein, we hypothesise that enhancing the propylene affinity of the adsorption sites while keeping a suitable pore size can address this challenge. To do so, we performed silver exchange of a commercial zeolite Y, thereby making the adsorbent design easily scalable. We characterised the adsorbent using analytical, spectroscopic and imaging tools, tested its equilibrium and dynamic sorption properties using volumetric and gravimetric techniques and compared its performance to those of state-of-the-art adsorbents as well as other silver-functionalised adsorbents. The silver-exchanged zeolite Y (Ag-Y) exhibited one of the best selectivity vs uptake performances reported so far. Ag-Y also displayed fast adsorption kinetics and reversible propylene sorption, making it a promising new benchmark for propylene/propane separation. Synchrotron-based pair distribution function analyses identified the silver cations’ location which confirmed that the silver sites are easily accessible to the adsorbates. This aspect can, in part, explain the propylene/propane separation performance observed. The overall design strategy proposed here to enhance sorption site affinity and maintain pore size could be extended to other adsorbents and support the deployment of adsorption technology for propylene/propane separation.
Schukraft GEM, Itskou I, Woodward RT, et al., 2022, Evaluation of CO2 and H2O Adsorption on a Porous Polymer Using DFT and In Situ DRIFT Spectroscopy, JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 126, Pages: 8048-8057, ISSN: 1520-6106
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Tian T, Xu J, Xiong Y, et al., 2022, Cu-functionalised porous boron nitride derived from a metal–organic framework, Journal of Materials Chemistry A, Vol: 10, Pages: 20580-20592, ISSN: 2050-7488
Porous boron nitride (BN) displays promising properties for interfacial and bulk processes, e.g. molecular separation and storage, or (photo)catalysis. To maximise porous BN's potential in such applications, tuning and controlling its chemical and structural features is key. Functionalisation of porous BN with metal nanoparticle represents one possible route, albeit a hardly explored one. Metal–organic frameworks (MOFs) have been widely used as precursors to synthesise metal functionalised porous carbon-based materials, yet MOF-derived metal functionalised inorganic porous materials remain unexplored. Here, we hypothesise that MOFs could also serve as a platform to produce metal-functionalised porous BN. We have used a Cu-containing MOF, i.e. Cu/ZIF-8, as a precursor and successfully obtained porous BN functionalised with Cu nanoparticles (i.e. Cu/BN). While we have shown control of the Cu content, we have not yet demonstrated it for the nanoparticle size. The functionalisation has led to improved light harvesting and enhanced electron–hole separation, which have had a direct positive impact on the CO2 photoreduction activity (production formation rate 1.5 times higher than pristine BN and 12.5 times higher than g-C3N4). In addition, we have found that the metal in the MOF precursor impacts porous BN's purity. Unlike Cu/ZIF-8, a Co-containing ZIF-8 precursor led to porous C-BN (i.e. BN with a large amount of C in the structure). Overall, given the diversity of metals in MOFs, one could envision our approach as a method to produce a library of different metal functionalised porous BN samples.
Azzan H, Rajagopalan AK, L'Hermitte A, et al., 2022, Simultaneous estimation of gas adsorption equilibria and kinetics of individual shaped adsorbents, Chemistry of Materials, Vol: 34, Pages: 6671-6686, ISSN: 0897-4756
Shaped adsorbents (e.g., pellets, extrudates) are typically employed in several gas separation and sensing applications. The performance of these adsorbents is dictated by two key factors, their adsorption equilibrium capacity and kinetics. Often, adsorption equilibrium and textural properties are reported for materials. Adsorption kinetics are seldom presented due to the challenges associated with measuring them. The overarching goal of this work is to develop an approach to characterize the adsorption properties of individual shaped adsorbents with less than 100 mg of material. To this aim, we have developed an experimental dynamic sorption setup and complemented it with mathematical models, to describe the mass transport in the system. We embed these models into a derivative-free optimizer to predict model parameters for adsorption equilibrium and kinetics. We evaluate and independently validate the performance of our approach on three adsorbents that exhibit differences in their chemistry, synthesis, formulation, and textural properties. Further, we test the robustness of our mathematical framework using a digital twin. We show that the framework can rapidly (i.e., in a few hours) and quantitatively characterize adsorption properties at a milligram scale, making it suitable for the screening of novel porous materials.
Taddei M, Petit C, 2022, Engineering metal-organic frameworks for adsorption-based gas separations: from process to atomic scale (vol 6, pg 841, 2021), MOLECULAR SYSTEMS DESIGN & ENGINEERING, Vol: 7, Pages: 1162-1162, ISSN: 2058-9689
Xiao F-S, Azevedo D, Nicholas CP, et al., 2022, Preface for Special Issue on Engineered Methodologies for CO2 Utilization, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 61, Pages: 10295-10297, ISSN: 0888-5885
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- Citations: 1
Hwang J, Azzan H, Pini R, et al., 2022, H2, N2, CO2, and CH4 unary adsorption isotherm measurements at low and high pressures on zeolitic imidazolate framework ZIF-8, Journal of Chemical & Engineering Data, Vol: 67, Pages: 1674-1686, ISSN: 0021-9568
Excess adsorption of CO2, CH4, N2, and H2 on ZIF-8 was measured gravimetrically in the pressure range ranging from vacuum to 30 MPa at 298.15, 313.15, 333.15, 353.15, and 394.15 K using a magnetic suspension balance. The textural properties of the adsorbent material─i.e., skeletal density, surface area, pore volume, and pore-size distribution─were estimated by helium gravimetry and N2 (77 K) physisorption. The adsorption isotherms were fitted with the Sips isotherm model and the virial equation, and the values of isosteric heat of adsorption and Henry constants for the gases were determined using the latter.
Osterrieth JWM, Rampersad J, Madden D, et al., 2022, How Reproducible are Surface Areas Calculated from the BET Equation?, ADVANCED MATERIALS, Vol: 34, ISSN: 0935-9648
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- Citations: 26
Shankar RB, Mistry EDR, Lubert-Perquel D, et al., 2022, A response surface model to predict and experimentally tune the chemical, magnetic and optoelectronic properties of oxygen-doped boron nitride, ChemPhysChem: a European journal of chemical physics and physical chemistry, Vol: 23, ISSN: 1439-4235
Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50–2.90 eV) and tuning of the oxygen (2–14 at.%) and specific paramagnetic OB3 contents (7–294 a.u. g−1). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.
Schukraft GEM, Moss B, Kafizas AG, et al., 2022, Effect of band bending in photoactive MOF-based heterojunctions., ACS Applied Materials and Interfaces, Vol: 14, Pages: 19342-19352, ISSN: 1944-8244
Semiconductor/metal-organic framework (MOF) heterojunctions have demonstrated promising performance for the photoconversion of CO2 into value-added chemicals. To further improve performance, we must understand better the factors which govern charge transfer across the heterojunction interface. However, the effects of interfacial electric fields, which can drive or hinder electron flow, are not commonly investigated in MOF-based heterojunctions. In this study, we highlight the importance of interfacial band bending using two carbon nitride/MOF heterojunctions with either Co-ZIF-L or Ti-MIL-125-NH2. Direct measurement of the electronic structures using X-ray photoelectron spectroscopy (XPS), work function, valence band, and band gap measurements led to the construction of a simple band model at the heterojunction interface. This model, based on the heterojunction components and band bending, enabled us to rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. Using the insight gained from a promising band bending diagram, we developed a Type II carbon nitride/MOF heterojunction with a 2-fold enhanced CO2 photoreduction activity compared to the physical mixture.
Heiba HF, Bullen JC, Kafizas A, et al., 2022, The determination of oxidation rates and quantum yields during the photocatalytic oxidation of As(III) over TiO2, Journal of Photochemistry and Photobiology A: Chemistry, Vol: 424, Pages: 113628-113628, ISSN: 1010-6030
The determination of reaction rates for the photocatalytic oxidation (PCO) of arsenite (As(III)) using TiO2 under UV radiation is challenging due to the numerous experimental processes. This includes chemical processes running simultaneously with PCO (e.g. adsorption of arsenic species, direct UV photolysis of As(III)) and the analytical approach used (e.g. whether As(III) or As(V) are measured and used in the calculation of the PCO rate). The various experimental approaches used to date have led to oxidation rates and rate constants which vary by orders of magnitude and contradicting information on rate laws. Here we present the results of a critical examination of possible controls affecting the experimental determination of PCO rates. First, we demonstrate that the choice of analytical technique is not critical, provided that the rate constants are calculated based on the depletion of As(III) after correction of the directly adsorbed As(III). Second, we show the correction of the directly adsorbed As(III) at each time interval is best done by running two parallel experiments (one under UV and the other in dark) instead of running sequential experiment (i.e. running the experiment in the dark then turning on the UV lamp). These findings are supported by XPS analysis of the oxidation state of TiO2-sorbed As. Third, we demonstrate that photolysis by the light source itself, as well as the chemical composition of the solution (i.e. the effect of HEPES and the ionic strength), can significantly increase As(III) oxidation rates and need to be corrected. Finally, to determine the quantum yield of As(III) oxidation, we measured the photon absorption by the TiO2 photocatalyst. Our results showed that the quantum yield (Ø) for this oxidation reaction was low, and in the region of 0.1 to 0.2 %.
Petit C, L'Hermitte A, Dawson D, et al., 2021, Formation mechanism and porosity development in porous boron nitride, The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, Vol: 125, Pages: 27429-27439, ISSN: 1932-7447
Porous boron nitride (BN) has proven promising as a novel class of inorganic materials in the field of separations and particularly adsorption. Owing to its high surface area and thermal stability, porous BN has been researched for CO2 capture and water cleaning, for instance. However, research remains at the laboratory scale due to a lack of understanding of the formation mechanism of porous BN, which is largely a “black box” and prevents scale up. Partial reaction pathways have been unveiled, but they omit critical steps in the formation, including the porosity development, which is key to adsorption. To unlock the potential of porous BN at a larger scale, we have investigated its formation from the perspective of both chemical formation and porosity development. We have characterized reaction intermediates obtained at different temperatures with a range of analytical and spectroscopic tools. Using these analyses, we propose a mechanism highlighting the key stages of BN formation, including intermediates and gaseous species formed in the process. We identified the crucial formation of nonporous carbon nitride to form porous BN with release of porogens, such as CO2. This work paves the way for the use of porous BN at an industrial level for gas and liquid separations.
Shankar R, Mistry E, Lubert-Perquel D, et al., 2021, A response surface model to predict and experimentally tune the chemical, magnetic and optoelectronic properties of oxygen-doped boron nitride
<jats:p>A new material platform for boron nitride (BN) as a heterogeneous photocatalyst for solar fuels synthesis has recently emerged. One of the bottlenecks of this material is the lack of photoactivity under visible light, which hinders its rate performance. Theoretical studies have predicted that tuning the oxygen content in oxygen-doped BN (BNO) might be used to lower and vary the band gap. However, this is yet to be verified experimentally. We present herein a systematic experimental route facilitating simultaneous tuning of the chemical, magnetic and optoelectronic properties of BNO using a multivariate synthesis parameter space. Deep visible range band gaps (1.50 – 2.90 eV) were experimentally achieved and tuned over an oxygen composition of 2 – 14 at. %, and specific paramagnetic OB3 content of 7 – 294 a.u. g-1, thus supporting theoretical predictions. Through designing a response surface via a design of experiments (DOE) process, the key synthesis parameters influencing the chemical, magnetic and optoelectronic properties of BNO were identified. In addition, model prediction equations relating the aforementioned properties to the synthesis parameter space are presented. Accurate model predictions for the oxygen content and band gap were conducted and validated experimentally. Such a methodology is valuable for further advances in tailoring and optimising BN materials for heterogeneous photocatalytic reactions.</jats:p>
Shankar R, Mistry E, Lubert-Perquel D, et al., 2021, A response surface model to predict and experimentally tune the chemical, magnetic and optoelectronic properties of oxygen-doped boron nitride
<jats:p>A new material platform for boron nitride (BN) as a heterogeneous photocatalyst for solar fuels synthesis has recently emerged. One of the bottlenecks of this material is the lack of photoactivity under visible light, which hinders its rate performance. Theoretical studies have predicted that tuning the oxygen content in oxygen-doped BN (BNO) might be used to lower and vary the band gap. However, this is yet to be verified experimentally. We present herein a systematic experimental route facilitating simultaneous tuning of the chemical, magnetic and optoelectronic properties of BNO using a multivariate synthesis parameter space. Deep visible range band gaps (1.50 – 2.90 eV) were experimentally achieved and tuned over an oxygen composition of 2 – 14 at. %, and specific paramagnetic OB3 content of 7 – 294 a.u. g-1, thus supporting theoretical predictions. Through designing a response surface via a design of experiments (DOE) process, the key synthesis parameters influencing the chemical, magnetic and optoelectronic properties of BNO were identified. In addition, model prediction equations relating the aforementioned properties to the synthesis parameter space are presented. Accurate model predictions for the oxygen content and band gap were conducted and validated experimentally. Such a methodology is valuable for further advances in tailoring and optimising BN materials for heterogeneous photocatalytic reactions.</jats:p>
Rajagopalan AK, Petit C, 2021, Material Screening for Gas Sensing Using an Electronic Nose: Gas Sorption Thermodynamic and Kinetic Considerations, ACS SENSORS, Vol: 6, Pages: 3808-3821, ISSN: 2379-3694
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- Citations: 3
Butler EL, Reid B, Luckham PF, et al., 2021, Interparticle Forces of a Native and Encapsulated Metal-Organic Framework and Their Effects on Colloidal Dispersion, ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 45898-45906, ISSN: 1944-8244
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- Citations: 2
Taddei M, Petit C, 2021, Engineering metal-organic frameworks for adsorption-based gas separations: from process to atomic scale, Molecular Systems Design & Engineering, Vol: 6, Pages: 841-875, ISSN: 2058-9689
Metal-organic frameworks (MOFs) are the object of intense research targeting their deployment as adsorbents for a wide range of gas separations, such as CO2 capture, biogas upgrading, air separation and small hydrocarbons separation. The scope of this review is to provide chemists, material scientists and engineers with an overview of the state-of-the-art and of the main challenges in the field of adsorption-based gas separations using MOFs. To do so, we first discuss current gas separation challenges for which adsorption could play a role. The following three sections of the paper describe process-level considerations in the design, selection and deployment of MOFs as sorbents and subsequently focus on material-level considerations. Both the process and the material aspects cover experimental and computational work. Going from the process scale to the atomic scale, we aim to highlight the links and synergies between the two and identify the current barriers that hamper the development of adsorption-based gas separations using MOFs as sorbents. Throughout the article, we also provide fundamental and technical information related to MOFs design, synthesis, characterisation and sorption testing.
Xiong Y, Woodward RT, Danaci D, et al., 2021, Understanding trade-offs in adsorption capacity, selectivity and kinetics for propylene/propane separation using composites of activated carbon and hypercrosslinked polymer, CHEMICAL ENGINEERING JOURNAL, Vol: 426, ISSN: 1385-8947
Rampal N, Ajenifuja A, Tao A, et al., 2021, The development of a comprehensive toolbox based on multi-level, high-throughput screening of MOFs for CO/N-2 separations, CHEMICAL SCIENCE, Vol: 12, Pages: 12068-12081, ISSN: 2041-6520
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Danaci D, Bui M, Petit C, et al., 2021, En route to zerio emissions for power and industry with amine-based post-combustion capture, Environmental Science and Technology (Washington), Vol: 55, Pages: 10619-10632, ISSN: 0013-936X
As more countries commit to a net-zero GHG emission target, we need a whole energy and industrial system approach to decarbonization rather than focus on individual emitters. This paper presents a techno-economic analysis of monoethanolamine-based post-combustion capture to explore opportunities over a diverse range of power and industrial applications. The following ranges were investigated: feed gas flow rate between 1–1000 kg ·s–1, gas CO2 concentrations of 2–42%mol, capture rates of 70–99%, and interest rates of 2–20%. The economies of scale are evident when the flue gas flow rate is <20 kg ·s–1 and gas concentration is below 20%mol CO2. In most cases, increasing the capture rate from 90 to 95% has a negligible impact on capture cost, thereby reducing CO2 emissions at virtually no additional cost. The majority of the investigated space has an operating cost fraction above 50%. In these instances, reducing the cost of capital (i.e., interest rate) has a minor impact on the capture cost. Instead, it would be more beneficial to reduce steam requirements. We also provide a surrogate model which can evaluate capture cost from inputs of the gas flow rate, CO2 composition, capture rate, interest rate, steam cost, and electricity cost.
Shankar R, Marchesini S, Muller EA, et al., 2021, Gas Adsorption in Amorphous Porous Boron Oxynitride: Grand Canonical Monte Carlo Simulations and Experimental Determination
<jats:p>Note: The authors realised errors in the calculations related to this study, which impact the conclusions of the work previously posted.</jats:p>
Tian T, Hou J, Ansari H, et al., 2021, Mechanically stable structured porous boron nitride with high volumetric adsorption capacity, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 13366-13373, ISSN: 2050-7488
Schukraft GEM, Woodward RT, Kumar S, et al., 2021, Hypercrosslinked polymers as a photocatalytic platform for visible-light-driven CO2 photoreduction using H2O, ChemSusChem: chemistry and sustainability, energy and materials, Vol: 14, Pages: 1720-1727, ISSN: 1864-5631
The design of robust, high‐performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2O. It is hypothesized that superior H2O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2. These polymers are an intriguing set of organic photocatalysts, displaying no long‐range order or extended π‐conjugation. The as‐synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar‐energy conversion.
Tian T, Hou J, Ansari H, et al., 2021, Mechanically Stable Monolithic Porous Boron Nitride with High Volumetric Adsorption Capacity
<jats:p>The development of adsorbents into structured and robust forms remains a challenge for emerging porous materials. In the context of porous boron nitride (BN), studies point to a tradeoff between mechanical stability, porosity, density, and adsorption kinetics. Approaches towards shaping and densification of porous BN have been mostly empirical since a detailed understanding of its formation mechanism, and how it impacts mechanical strength and porosity, is lacking. Here, we demonstrate a synthesis method that can directly produce a mechanically robust monolithic porous BN (mpBN) from an easily scalable polymeric precursor, which results in the highest volumetric surface area among porous BN samples to date. mpBN exhibits a high bulk density, 50% higher than BN powders and over ten times higher than the structured BN aerogels, while maintaining fast sorption kinetics. mpBN presents good mechanical strength, with hardness of 66.4 ± 4.5 MPa, <jats:italic>i.e. </jats:italic>one to two orders of magnitude higher than structured aerogels. We propose a mpBN formation mechanism which reveals that the crosslinked intermediates are responsible for the high mechanical strength of the final material. Our approach produces a form of BN that addresses the limitations of other adsorbents, and facilitate their application in gas separation and storage technologies. </jats:p><jats:p />
Stafford J, Uzo N, Farooq U, et al., 2021, Real-time monitoring and hydrodynamic scaling of shear exfoliated graphene, 2D Materials, Vol: 8, Pages: 1-17, ISSN: 2053-1583
Shear-assisted liquid exfoliation is a primary candidate for producing defect-free two-dimensional (2D) materials. A range of approaches that delaminate nanosheets from layered precursors in solution have emerged in recent years. Diverse hydrodynamic conditions exist across these methods, and combined with low-throughput, high-cost characterization techniques, strongly contribute to the wide variability in performance and material quality. Nanosheet concentration and production rate are usually correlated against operating parameters unique to each production method, making it difficult to compare, optimize and predict scale-up performance. Here, we reveal the shear exfoliation mechanism from precursor to 2D material and extract the derived hydrodynamic parameters and scaling relationship that are key to nanomaterial output and common to all shear exfoliation processes. Our investigations use conditions created from two different hydrodynamic instabilities—Taylor vortices and interfacial waves—and combine materials characterization, fluid dynamics experiments and numerical simulations. Using graphene as the prototypical 2D material, we find that scaling of concentration of few-layer nanosheets depends on local strain rate distribution, relationship to the critical exfoliation criterion, and precursor residence time. We report a transmission-reflectance method to measure concentration profiles in real-time, using low-cost optoelectronics and without the need to remove the layered precursor material from the dispersion. We show that our high-throughput, in situ approach has broad uses by controlling the number of atomic layers on-the-fly, rapidly optimizing green solvent design to maximize yield, and viewing live production rates. Combining the findings on the hydrodynamics of exfoliation with this monitoring technique, we unlock targeted process intensification, quality control, batch traceability and individually customizable 2D materials on-demand.
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